diff --git a/src/unix/bsd/apple/b64.rs b/src/unix/bsd/apple/b64.rs
index 327a4b63116b076b16ee8af45d5a09b4c4ebd0e6..3f83230805fe3ad22f8ed6caeba92e05e1321a5d 100644
--- a/src/unix/bsd/apple/b64.rs
+++ b/src/unix/bsd/apple/b64.rs
@@ -17,3 +17,5 @@ pub const __PTHREAD_RWLOCK_SIZE__: usize = 192;
 
 pub const TIOCTIMESTAMP: ::c_ulong = 0x40107459;
 pub const TIOCDCDTIMESTAMP: ::c_ulong = 0x40107458;
+
+pub const FIONREAD: ::c_ulong = 0x4004667f;